Production tubing shut valves have been used for a number of years to protect submersible well pumps from back flow. A typical submersible pump assembly includes a pumping section that is placed within a well and takes suction directly from the well. The pumping section is often a centrifugal or a progressive cavity pump, however linear pumps are also employed. The pump assembly is usually suspended on a string of tubing that extends into the cased well. The pump discharges well fluid up the tubing.
When the pump shuts down, fluid may flow back down through the tubing and the intake of the pump, possibly spinning the pump in reverse. The downward flow occurs until the level of fluid in the tubing equals the level in the tubing annulus surround the tubing. The downward flow through the pump may bring debris in the tubing back into the pump, causing damage on later restarting. In other cases, downward flow simply stops, allowing solids to settle out from the long vertical section of production tubing on top of or in the pump. The tubing string or the pump can pack off or plug after such shut down. If the tubing does not drain, the operator may then have to bail out the production fluid before pulling the pump and tubing. Bailing involves running a bailer on a wire line relatedly down into the tubing, taking time.
In a current design, the pump assembly has a diverter valve that drains the tubing above the pump when the pump shuts down. The diverter valve has a valve housing installed with the tubing string above the pump. The valve housing has an interior in communication with fluid in the string of tubing above the valve housing. The valve housing has a shunt port communicating the interior of the valve housing with an annulus surround the string of tubing. A valve shuttle is slidably received within the valve housing for movement between upper and lower positions. The valve shuttle blocks communication through the shunt port while in the upper position, and while in the lower position, opens the shunt port. A float, also called a floating ring, is located in the upper portion of the shuttle valve assembly, the upper portion being referred to herein as a flow tube. If the pump is a progressing cavity type, the floating ring slides up and down a connector or polished rod extending upward from the pump. The polished rod is connected to a string of rotatable drive rods extending down the production tubing. When there is no flow or reverse flow, the floating ring slides down the polished rod and sits on top of the valve shuttle, pushing it down and opening the shut ports to allow fluid to drain out of the production tubing.
When the pump is again started, fluid flow acts on the floating ring to slide it upward along the polished rod within the flow tube. The flow tube is typically two to ten feet long. The flow tube inner diameter is larger than the production tubing inner diameter and through-bore of the diverter valve. Under normal flow velocities, the floating ring will rise a few feet. The larger inner diameter flow tube typically lowers the velocity of the fluid and allows the floating ring to stop rising.